1. Field of the Invention
The invention relates to a method of neutralizing acid solutions of alkyl polyglycosides having alkyl groups with 8-24 C atoms in alcohols having 8-24 C atoms.
2. Discussion of the Background
Alkyl polyglycosides are nontoxic and readily degradable surfactants. Accordingly, they are used as detergents and cleaning agents, and also as emulsifiers and dispersants. However, they only have the desired interfacial properties if the alkyl groups contain at least 8 C atoms.
Alkyl glycosides and alkyl polyglycosides with long chain alkyl groups are generally manufactured by multi-step syntheses. EP-A-0 306 652 discloses a two-stage method in which an n-butylglycoside is produced by glycosidation of n-butanol, and then the desired long chain alkyl polyglycoside is produced by transglycosidation with a long chain alcohol. Both glycosidation and transglycosidation reactions are catalyzed by acids. After completion of the transglycosidation, the mixture is neutralized, and the excess long chain alcohol is distilled off.
Single-step reactions for manufacturing alkyl polysaccharides are known. U.S. Pat. No. 3,839,318 discloses a process for directly reacting saccharides with long chain alcohols, under special reaction conditions. The mixture must be neutralized after completion of the reaction, and the excess long chain alcohol is subsequently distilled off.
EP-A-0 249 013 recognizes that the degree of polymerization of alkyl polyglycosides can be influenced during transglycosidation by the amount of acid added. Here the mixture is neutralized after completion of the transglycosidation. Sodium hydroxide is used in an amount equivalent to the amount of sulfuric acid used. However, this technique is too imprecise for accurate adjustment to a desired pH value. For example, it does not take into account losses of acid which can occur by esterification.
Because saccharides readily thermally decompose in acid medium, the acid present prior to the distillation-off of the excess alcohols must be neutralized at least to a major extent. Such neutralization presents a problem, because it is not possible to directly measure the pH value of a fatty alcohol solution.